Without limiting the scope of the invention, its background is described in connection with electrode materials for use in a system, method and apparatus, as an example.
The rechargeable lithium-ion batteries (hereinafter collectively referred to as a “Secondary Cell”) are characterized by small size and high output voltage, allowing them to be used in a variety of devices, e.g., portable electronic devices such as cellular phones, laptop computers, digital video recorders and cordless power tools. The charge/discharge step in Secondary Cells is the result of exchange of lithium ions between a cathode and an anode. Generally, the main principle behind the chemical reaction is one where lithium in the positive electrode material is ionized during charge and moves to the negative electrode, while during discharge the Li ions move to the positive electrode.
In Secondary Cells, the action of charge/discharge is done through exchange of lithium ions between cathode and anode, thus the electrode composition is more important for deciding the battery performance. Secondary Cell performance is greatly affected by the composition of the cathode; and as a result, the cathode composition has been the subject of intensive research and development to examine electrode materials that optimize the discharge capacity, charge-discharge voltage, cycle life characteristics and storage characteristics.
The discharge capacity is a function of the amount of lithium ion exchanged whereas the discharge voltage is defined by materials and its crystal structures. As a result, cathodes materials common in the art include transition-metal oxide containing lithium, e.g., layered oxides such as lithium cobalt oxide (LixCoO2), spinels such as lithium manganese spinel (LixMn2O4) and olivines such as a lithium ion phosphate (LixFe(PO4)).
Conventional lithium-ion Secondary Cells use a carbon black or coke material into which lithium is inserted reversibly as the anode and a layered or framework transition-metal oxide is used as the cathode host material. The general structure of the electrode provides interstitial space for reversible lithium-ion insertion and extraction.
An electrochemically inactive material (e.g., carbon black or coke) that is chemically inert, conductive, soft and light-weight (normally carbon black) is added to a cathode material in order to maintain electrical contact between the small, dispersed transition-metal oxide cathode particles and the particles of the external circuit. Current technology also uses a binder (normally PTFE) as a cathode material additive in order to hold the composite cathode mass together, while allowing the electrolyte access to the surfaces of the oxide particles.
The foregoing stratigies have been recognized for many years; and while numerous solutions have been proposed, none of them adequately address the problem of optimizing the several functions of the composite cathode; viz. (1) allowing access of the electrolyte to the surface of the electrochemically active transition-metal oxide, (2) providing electrical contact between particles and between the particles and the current collector, and (3) holding the cathode mass together during repeated charge/discharge cycles. Moreover, substituting a conductive, electrochemically active, and electrically attached material for the electrochemically inactive, physically attached carbon black and PTFE would also enhance the capacity as well as the cycle life of the battery.